September 10, 1909] 



SCIENCE 



345 



oxidases and peroxidases ; and the possible in- 

 terrelations of enzymes and functional capac- 

 ity. Chapters on the constitution and mode of 

 action of enzymes present numerous newer 

 aspects of study — the identity of rennin and 

 proteolytic enzymes, their adsorption phe- 

 nomena, the laws of enzyme action, and its 

 reversibility, etc. A final chapter deals with 

 some of the more obscure relations of enzymes 

 to protoplasm and their environment. 



Dr. Vernon distinguishes the intracellular 

 enzymes from the exo-enzymes found in many 

 secretions " by reason of the facts that they 

 are bound up in the protoplasm of the cells, 

 and, so long as these cells retain their vitality, 

 can only exert their activity intracellularly." 

 It is perhaps doubtful whether a rigid defini- 

 tion of this sort can be successfully defended. 

 The author at any rate has extended his dis- 

 cussion in places beyond the bounds of strictly 

 intracellular functions; and he has dispelled 

 the fear that " the subject of these lectures 

 might at first sight be regarded as too small 

 and unimportant to warrant their reproduc- 

 tion in book form." They are entertaining as 

 well as helpful. Incidentally, as a specimen of 

 good book-making the volume is in striking 

 contrast to the average American product. 

 Lafayette B. Mendel 



Sheffield Scientific School, 

 Yaue Univebsity 



Tlankton Investigations of the Danish Lalces. 



By C. Wesenberg-Lund. Copenhagen, 1908. 



Pp. xii -\- 389. Appendix with forty-six 



tables. 



This is the second volume from the pen of 

 Dr. Wesenberg-Lund dealing with the investi- 

 gations that have been made at the Danish 

 Freshwater Laboratory. In the first volume, 

 published in 1904, the plankton is treated 

 chiefly from the qualitative and quantitative 

 standpoints. In the present one the origin 

 and variation of the Baltic fresh-water plank- 

 ton forms are discussed. The variations have 

 been studied by statistical methods in a large 

 amount of material that was collected during 

 a period of ten years. 



The author attributes seasonal variations to 



the increase in the temperature of the water 

 in the spring which lowers its specific gravity 

 and viscosity, thus increasing the rate of sink- 

 ing of plankton organisms. In response to 

 this change, the organisms increase their 

 buoyancy by adaptations which tend to pre- 

 vent accelerated sinking. The rate of sink- 

 ing of an organism depends upon its over- 

 weight, that is, how much heavier it is than 

 the water, its form and relative superficial 

 area, and the viscosity of the water. The 

 first two, over-weight and form-resistance, are 

 the biological factors involved and are con- 

 ditioned by the organism itself. Buoyancy 

 may be increased by reducing the over-weight, 

 or by increasing the form-resistance. The 

 latter may be increased by enlarging the rela- 

 tive surface through a decrease in volume, by 

 enlarging the absolute surface through an 

 increase in the longitudinal axis or the forma- 

 tion of processes, or by gelatinous coverings. 

 Such adaptations constitute seasonal varia- 

 tions and these are discussed in Chapters II. 

 to XI. 



Among the diatoms, it was found that 

 Tabellaria and Asierionella form chains in the 

 spring but they become stellate in summer. 

 There are variations in the size of the cell, 

 also, which are not seasonal but which seem to 

 have a cycle of four to five years. 



In C'eratium hirundinella the individuals 

 are comparatively small in April and early 

 May and at this time a fourth horn may be 

 entirely absent or only feebly developed. In 

 late May and in June there is a very consider- 

 able increase in size (100/x in length in a 

 month) and a fourth horn suddenly develops. 

 In the latter part of July and in August, the 

 individuals decrease in size and the fourth 

 horn nearly or entirely disappears. 



Definite seasonal variations were found in 

 only two rotifers, Anurwa cochlearis and 

 Asplanchna. The variations begin in May 

 and June and the individuals differ most from 

 the typical, or winter form, when the water 

 reaches its highest temperature. Late in the 

 autumn they return again to their normal ap- 

 pearance. 



Dr. Wesenberg-Lund thinks there is ample 

 justification for the reduction of the pond and 



